Corncobs are distinct morphological units formed by the ordered coaggregation of a filamentous microorganism and streptococci. At saturating numbers the adherent streptococci coat the surface of the filament so that the complex resembles an ear of corn. These corncob structures have been observed in developing or maturing human dental plaque and it has been suggested that corncob formation represents a connecting link between supra- and subgingival plaque. Our earlier work has shown that Fusobacterium nucleatum,an anaerobic gram-negative bacterium thought to be involved in some forms of periodontal disease, has the ability to form corncobs, in vitro, with strains of Streptococcus sanguis. One objectives are to characterize the previously identified corncob-receptor of F. nucleatum ATCC 10953, construct immunological and genetic probes for the detection and analysis of this receptor, and develop strategies designed to inhibit or block the corncob reaction in vitro. An active tryptic polypeptide of the proposed corncob receptor will be isolated on a preparative scale by immunoaffinity chromatography using monospecific polyclonal antibodies. The polypeptide will be characterized using classical biochemical procedures and the amino terminal portion of the molecule will be sequenced. Information derived from this sequence will be applied to the production of DNA hybridization probes which will be used for both the detection of the cloned structural gene, in recombinant plasmids, and the determination of the distribution of this specific corncob receptor in oral clinical isolates of Fusobacterium nucleatum. The anti-receptor antibodies and selected peptides, derived from the proteolytic digestion of the receptor protein will be evaluated, in competition and direct binding studies, for the ability to prevent corncob formation in vitro. Development and application of immunological and genetic probes should greatly enhance our ability to define the complex intergeneric coaggregation mechanisms that occur in the oral cavity. Furthermore, the results should lead to the production bf reagents which could be used to prevent the maturation of plaque and reduce the incidence of one possible inflammatory mechanism associated with the progression of gingivitis and periodontitis.